Industrial controllers are special-purpose computers utilized for controlling industrial processes, manufacturing equipment, and other factory automation, such as data collection or networked systems. In accordance with a control program, the industrial controller, having an associated processor (or processors), measures one or more process variables or inputs reflecting the status of a controlled system, and changes outputs effecting control of such system. The inputs and outputs may be binary, (e.g., on or off), as well as analog inputs and outputs assuming a continuous range of values.
Measured inputs received from such systems and the outputs transmitted by the systems generally pass through one or more input/output (I/O) modules. These I/O modules serve as an electrical interface to the controller and may be located proximate or remote from the controller including remote network interfaces to associated systems. Inputs and outputs may be recorded in an I/O table in processor memory, wherein input values may be asynchronously read from one or more input modules and output values written to the I/O table for subsequent communication to the control system by specialized communications circuitry (e.g., back plane interface, communications module). Output modules may interface directly with one or more control elements, by receiving an output from the I/O table to control a device such as a motor, valve, solenoid, amplifier, and the like.
At the core of the industrial control system, is a logic processor such as a Programmable Logic Controller (PLC) or PC-based controller. Programmable Logic Controllers for instance, are programmed by systems designers to operate manufacturing processes via user-designed logic programs or user programs. The user programs are stored in memory and generally executed by the PLC in a sequential manner although instruction jumping, looping and interrupt routines, for example, are also common. Associated with the user program are a plurality of memory elements or variables that provide dynamics to PLC operations and programs. These variables can be user-defined and can be defined as bits, bytes, words, integers, floating point numbers, timers, counters and/or other data types to name but a few examples.
Many industries such as chemical, pharmaceutical and other process applications employ PLC's and associated modules to automatically manufacture a plurality of various products. However, these type industries are often highly regulated and generally require extensive documentation of the overall manufacturing process in order to provide controls on the quality of products that are produced (e.g., controls regulating manufacturing processes in order to facilitate public safety). One such regulation relates to FDA regulation “21 CFR Part 11” that outlines an electronic validation procedure when documenting corresponding changes to such processes. For example, this includes how records are kept, who can access such records, and what procedures/controls are designed to ensure the authenticity, integrity, and, when appropriate, the confidentiality of electronic records.
Some attempts have been made at achieving compliance with the above noted regulation, whereby records of program changes may be generated after an editing procedure has already occurred to a program and often at a time that is far removed from the actual time of change. One example is that in some applications, a program change is recorded as part of a check-in procedure to a database which may occur well after the change has been made and may only reflect the final product of such changes. Thus, intermediate changes or other program interactions may go unrecorded. In contrast, given the discrete and real time nature of PLC systems, however, often times changes occur to various aspects of the PLC system that can have an immediate consequence on the system, yet not translate into an actual change to the underlying PLC program. For example, such changes can include real time forcing operations, wherein a bit may be forced to a value other than what the underlying logic has determined. Other changes such as clearing/setting a counter, register, and/or status area of PLC memory can also produce dramatic, process-changing results. In view of time sensitive transactions or changes that can occur in PLC-driven systems and the above regulations, there is a need for automated systems or components that can document changes in a more real time and controlled manner.